Conversion of uranium hexafluoride and recovery of uranium from ionic liquids

ABSTRACT

Described are methods for the recovery of uranium from uranium hexafluoride dissolved directly into ionic liquids.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under contract numberDE-NA0003624, subcontract 159313, awarded by the Department of Energy.The government has certain rights in the invention.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a U.S. national stage entry of International PatentApplication No. PCT/US2019/024870, filed on Mar. 29, 2019, the entirecontents of which are fully incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to methods for recovery of uranium fromuranium hexafluoride.

BACKGROUND OF THE INVENTION

Uranium hexafluoride (UF₆) is a highly volatile and reactive form ofuranium that is part of the national stockpile of nuclear materials.Ninety-five percent of the world-wide depleted uranium is in the form ofUF₆. There is a need to convert reactive UF₆ into more stable materialsthat can be utilized in subsequent applications. However, UF₆ reactsviolently with water producing uranyl fluoride and hydrofluoric acid(HF), and is extremely volatile and sublimes at room temperature.

Therefore, there remains a need for methods that safely transform UF₆that are required to deal with the large stockpile of material currentlyavailable worldwide.

BRIEF SUMMARY OF THE INVENTION

The disclosure provide methods for recovering uranium.

In one aspect, the methods comprise dissolving uranium hexafluoride(UF₆) directly into an ionic liquid at concentrations greater than OMand less than or equal to 0.5M; and applying a potential to the ionicliquid to deposit uranium onto an electrode as a metal.

In another aspect, the methods comprise dissolving uranium hexafluoride(UF₆) directly into an ionic liquid solvent at concentrations ≥0.5M toform a solid precipitate in an ionic liquid solution; separating thesolid precipitate from the ionic liquid solution; and thermal processingthe solid precipitate.

Other aspects and embodiments of the disclosure will become apparent inlight of the following description and drawings.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 is images showing the electrochemical recovery of uranium from anionic liquid. The left panel is an image of the electrochemical reactionin which uranium deposits are formed on the electrode. The right imageis scanning electron microscopy image of the uranium deposits.

FIG. 2A and FIG. 2B are Scanning Electron Microscopy (SEM) images ofuranium metal crystals. Box in FIG. 2B notes the geometric metalcrystals.

FIG. 3 is Energy Dispersive X-Ray Spectroscopy (EDS) maps for uranium,oxygen, fluorine, carbon and sulfur.

FIG. 4 is SEM images of the uranium deposits following electrochemicaldeposition from UF₆ in IL.

FIG. 5 shows elemental analysis of the uranium deposits of FIG. 4.

FIG. 6 is a powder X-ray diffraction (PXRD) pattern of the uraniumprecipitate.

FIG. 7 is a graph of the simultaneous thermogravimetry & differentialscanning calorimetry (TGA(green)/DSC (blue)) analysis of the uraniumprecipitate.

FIG. 8 is a PXRD pattern of the uranium precipitate following TGA. UO2is UO₂, and UO1 indicates that the uranium and oxygen atoms are slightlyless than a 1:2 ratio. The sulfur in UOS is likely from residual TFSI.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure provides methods for recovery of uranium fromuranium hexafluoride. The direct dissolution of uranium hexafluoride hasbeen achieved in ionic liquids (ILs) without any further chemicalmodifications. In addition, the uranium hexafluoride was chilled priorto dissolution in the IL to ensure the material was not volatilized. Thedissolution results in reduction of uranium hexafluoride to, the muchmore stable and relatively benign, uranium tetrafluoride. Two recoverypaths for the uranium have been achieved following dissolution:precipitation and electrochemical reduction. Both methods provide a pathto safely transform UF₆ and recover useful forms of uranium.

1. Definitions

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art. In case of conflict, the present document, includingdefinitions, will control. Preferred methods and materials are describedbelow, although methods and materials similar or equivalent to thosedescribed herein can be used in practice or testing of the presentinvention. All publications, patent applications, patents and otherreferences mentioned herein are incorporated by reference in theirentirety. The materials, methods, and examples disclosed herein areillustrative only and not intended to be limiting.

All methods described herein can be performed in any suitable orderunless otherwise indicated herein or otherwise clearly contradicted bycontext. The use of any and all examples, or exemplary language (e.g.,“such as”) provided herein, is intended merely to better illuminate theinvention and does not pose a limitation on the scope of the inventionunless otherwise claimed. No language in the specification, and nostructures shown in the drawings, should be construed as indicating thatany non-claimed element is essential to the practice of the invention.

The terms “comprise(s),” “include(s),” “having,” “has,” “can,”“contain(s),” and variants thereof, as used herein, are intended to beopen-ended transitional phrases, terms, or words that do not precludethe possibility of additional acts or structures. The singular forms“a,” “an” and “the” include plural references unless the context clearlydictates otherwise. The present disclosure also contemplates otherembodiments “comprising,” “consisting of,” and “consisting essentiallyof” the embodiments or elements presented herein, whether explicitly setforth or not.

The modifier “about” used in connection with a quantity is inclusive ofthe stated value and has the meaning dictated by the context (forexample, it includes at least the degree of error associated with themeasurement of the particular quantity). The modifier “about” shouldalso be considered as disclosing the range defined by the absolutevalues of the two endpoints. For example, the expression “from about 2to about 4” also discloses the range “from 2 to 4.” The term “about” mayrefer to plus or minus 10% of the indicated number. For example, “about10%” may indicate a range of 9% to 11%, and “about 1” may mean from0.9-1.1. Other meanings of “about” may be apparent from the context,such as rounding off, so, for example “about 1” may also mean from 0.5to 1.4.

For the recitation of numeric ranges herein, each intervening numberthere between with the same degree of precision is explicitlycontemplated. For example, for the range of 6-9, the numbers 7 and 8 arecontemplated in addition to 6 and 9, and for the range 6.0-7.0, thenumber 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 areexplicitly contemplated.

For purposes of this disclosure, the chemical elements are identified inaccordance with the Periodic Table of the Elements, CAS version,Handbook of Chemistry and Physics, 75th Ed., inside cover, and specificfunctional groups are generally defined as described therein.Additionally, general principles of organic chemistry, as well asspecific functional moieties and reactivity, are described in OrganicChemistry, Thomas Sorrell, University Science Books, Sausalito, 1999;Smith and March March's Advanced Organic Chemistry, 5th Edition, JohnWiley & Sons, Inc., New York, 2001; Larock, Comprehensive OrganicTransformations, VCH Publishers, Inc., New York, 1989; Carruthers, SomeModern Methods of Organic Synthesis, 3rd Edition, Cambridge UniversityPress, Cambridge, 1987; the entire contents of each of which areincorporated herein by reference.

The term “alkyl,” as used herein, means a straight or branched,saturated hydrocarbon chain. Representative examples of alkyl include,but are not limited to, methyl, ethyl, n-propyl, iso-propyl, n-butyl,sec-butyl, iso-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl,n-hexyl, 3-methylhexyl, 2,2-dimethylpentyl, 2,3-dimethylpentyl,4,4-dimethylpentan-2-yl, n-heptyl, n-octyl, n-nonyl, and n-decyl.

The term “substituted” refers to a group that may be further substitutedwith one or more non-hydrogen substituent groups. For example,alkyl-substituted ammonium cations refer to an ammonium group which maybe substituted with at least one alkyl group, as described herein. Insome embodiments, a group may be substituted with two alkyl groups, suchthat it is dialkyl substituted, or four alkyl group, such that it istetraalkyl substituted.

The term “ionic liquid” or “IL” refers to a salt which melts at arelatively low temperature. An ionic liquid is essentially a salt in theliquid state. Some ionic liquids are room temperature ionic liquids or“RTILs” which indicates they are liquids at room temperature. Whileordinary liquids such as water and gasoline are predominantly made ofelectrically neutral molecules, ionic liquids are largely made of ionsand ion pairs (i.e., cations and anions). The physical properties of anIL vary with the identity of the cation/anion species. Any salt thatmelts without decomposing or vaporizing can usually yield an ionicliquid. Sodium chloride (NaCl), for example, melts at 801° C. (1,474°F.) into a liquid that consists largely of sodium cations (Na+) andchloride anions (Cl−).

The term “reductive decomposition” refers generally to theelectrochemical stability of solvent molecules, such that atincreasingly negative (reducing) potentials the molecules becomeunstable and decompose. Herein, the solvent molecules are the ionicliquids.

2. Methods

The present disclosure provides methods for recovering uranium. In oneaspect, the methods comprise an electrochemical reduction. In anotheraspect, the methods comprise precipitation of a uranium salt, which maybe further refined to uranium metal.

a. Electrochemical Reduction

The method to recover uranium may comprise dissolving uraniumhexafluoride (UF₆) directly into an ionic liquid at concentrationsgreater than 0 M and less than or equal to 0.5 M and applying apotential to the ionic liquid to deposit uranium onto an electrode as ametal. The method may further comprise chilling the UF₆ prior todissolving the UF₆ in the ionic liquid.

The concentration of uranium hexafluoride (UF₆) in the ionic liquidsolvent may be less than or equal to 0.5 M, less than or equal to 0.4 M,less than or equal to 0.3 M, less than or equal to 0.2 M, less than orequal to 0.1 M, less than or equal to 0.01 M or less than or equal to0.005 M. The concentration of uranium hexafluoride (UF₆) in the ionicliquid solvent may be greater than 0 M, greater than 0.005 M, greaterthan 0.01 M, greater than 0.1 M, greater than 0.2 M, greater than 0.3 M,or greater than 0.4 M.

The ionic liquid may be any combination of cation and anion. Thecombination of cation and anion may be chosen to influence theproperties of the solution as necessary for optimization of the methodsdescribed herein. The ionic liquid may be a room temperature ionicliquid (RTIL). RTILs are those liquid at room temperature. RTILs havesimilar electrochemical properties of other ionic liquids without theneed for elevated temperatures, and the large potential window of RTILsolutions is beneficial for electrochemical reduction.

The ionic liquid may be a simple ionic liquid, containing one type ofcation with one type of anion. The ionic liquid may be a complex ormixed ionic liquid, containing several types of anions and cations ordouble salts.

The ionic liquid may comprise an anion with a lone pair of electrons. Insome embodiments the anion is selected from the group consisting ofn-bis(trifluoromethanesulfonylimide) (TFSI), dicyanomide,trifluoroacetate, alkyl sulfonates, alkyl sulfates,bis(fluorosulfonyl)imide, and trifluoromethylacetate. In exemplaryembodiments, the ionic liquid comprises an-bis(trifluoromethanesulfonylimide) (TFSI) anion.

The stability of the ionic liquid needs to be appropriate for theelectrochemical deposition of uranium. Cations and anions of ionicliquids may undergo decomposition at various potential values. In someembodiments, the ionic liquid comprises a cation that is stable and doesnot undergo reductive decomposition at a potential between −2 and −4Volts. The cation may be selected from the group consisting ofalkyl-substituted or unsubstituted ammonium cations, alkyl-substitutedor unsubstituted piperidinium cations, and alkyl-substituted orunsubstituted pyrrolidinium cations. In some embodiments, the cation isselected from the group consisting of tetraalkylammonium cation, adialkylpiperidinium cation, and dialkylpyrrolidinium cation. Inexemplary embodiments, the ionic liquid comprises a methylpropylpiperidinium cation.

The applied potential may be any potential which allows the depositionof uranium onto an electrode as a metal. The applied potential may bemore negative than −2 Volts. The applied potential may be more negativethan −2.25 Volts, −2.5 Volts, −2.75 Volts, −3 Volts, −3.25 Volts, −3.5Volts, −3.75 Volts or −4 Volts. In some embodiments, the appliedpotential is pulsed. In some embodiments, the applied potential isconstant.

b. Precipitation

The method to recover uranium may comprise the methods comprisedissolving uranium hexafluoride (UF₆) directly into an ionic liquid atconcentrations greater than or equal to 0.5 M to form a solidprecipitate in an ionic liquid solution, separating the solidprecipitate from the ionic liquid solution, and thermal processing thesolid precipitate. The method may further comprise chilling the UF₆prior to dissolving the UF₆ in the ionic liquid.

In some embodiments, the thermal processing is under an inert atmosphereto form uranium metal. In some embodiments, the thermal processing isunder an ambient atmosphere to form uranium oxide, UO₂.

The concentration of uranium hexafluoride (UF₆) into the ionic liquidsolvent may be greater than 0.5 M, greater than 0.75 M, greater than 1M, greater than 1.25 M, greater than 1.5 M, or greater than 2.0 M. Theconcentration of uranium hexafluoride (UF₆) into the ionic liquidsolvent may be less than 2.4 M, less than 2.0 M. less than 1.5 M, lessthan 1.25 M, less than 1 M, or less than 0.75 M.

The ionic liquid may be any combination of cation and anion. Thecombination of cation and anion may be chosen to influence theproperties of the solution as necessary for optimization in the methodsdescribed herein. The ionic liquid may be a room temperature ionicliquid (RTIL). RTILs are those liquid at room temperature. RTILs havesimilar electrochemical properties of other ionic liquids without theneed for elevated temperatures.

The ionic liquid may be a simple ionic liquid, containing one type ofcation with one type of anion. The ionic liquid may be a complex ormixed ionic liquid, containing several types of anions and cations ordouble salts.

The ionic liquid may comprise an anion with a lone pair of electrons. Insome embodiments the anion is selected from the group consisting ofn-bis(trifluoromethanesulfonylimide) (TFSI), dicyanomide,trifluoroacetate, alkyl sulfonates, alkyl sulfates,bis(fluorosulfonyl)imide, and frifluoromethylacetate. In exemplaryembodiments, the ionic liquid comprises an-bis(trifluoromethanesulfonylimide) (TFSI) anion.

The solid precipitate may be a salt comprising the cation of the ionicliquid and a reduced form of the uranium hexafluoride (UF₆ ²⁻). Theionic liquid may comprise a cation that has a charge such that the saltwhich forms between the cation and reduced UF₆ ²⁻ is charge neutral.

In some embodiments, the precipitate comprises a salt of a uraniumhexafluoro anion and the ionic liquid cation. In some embodiments, theionic liquid solution comprises uranium hexafluoride dissolved in theionic liquid.

Thermal processing of the solid precipitate may be completed by any ofthe known methods in the art, such as use of a melting furnace. In someembodiments, the thermal processing may be done under an inertatmosphere to form uranium metal. In some embodiments, the thermalprocessing may be done under an oxygen containing atmosphere to form auranium oxides.

In some embodiments, the ionic liquid solution comprises uraniumhexafluoride dissolved in the ionic liquid. In some embodiments, themethod further comprises applying a potential to the ionic liquidsolution after separation of the solid precipitate to deposit theremaining uranium in the ionic liquid solution onto an electrode as ametal. The applied potential may be any potential which allows thedeposition of uranium onto an electrode as a metal. The appliedpotential may be more negative than −2 Volts. The applied potential maybe more negative than −2.25 Volts, −2.5 Volts, −2.75 Volts, −3 Volts,−3.25 Volts, −3.5 Volts, −3.75 Volts or −4 Volts. In some embodiments,the applied potential is pulsed. In some embodiments, the appliedpotential is constant.

The stability of the ionic liquid needs to be appropriate for theelectrochemical deposition of uranium. Cations and anions of ionicliquids may undergo decomposition at various potential values. In someembodiments, the ionic liquid comprises a cation that is stable and doesnot undergo reductive decomposition at a potential between −2 and −4Volts. The cation may be selected from the group consisting ofalkyl-substituted or unsubstituted ammonium cations, alkyl-substitutedor unsubstituted piperidinium cations, and alkyl-substituted orunsubstituted pyrrolidinium cations. In some embodiments, the cation isselected from the group consisting of tetraalkylammonium cation, adialkylpiperidinium cation, and dialkylpyrrolidinium cation. Inexemplary embodiments, the ionic liquid comprises a methylpropylpiperidinium cation.

3. Examples

It will be readily apparent to those skilled in the art that othersuitable modifications and adaptations of the methods of the presentdisclosure described herein are readily applicable and appreciable, andmay be made using suitable equivalents without departing from the scopeof the present disclosure or the aspects and embodiments disclosedherein. Having now described the present disclosure in detail, the samewill be more clearly understood by reference to the following examples,which are merely intended only to illustrate some aspects andembodiments of the disclosure, and should not be viewed as limiting tothe scope of the disclosure. The disclosures of all journal references,U.S. patents, and publications referred to herein are herebyincorporated by reference in their entireties.

Example 1: UF₆ Dissolution in Ionic Liquids

Dissolution Process: A closed and sealed vessel of UF₆ was cooled in aliquid nitrogen well within a glovebox for several hours to ensure thespecies was solid. The vessel was unsealed and the UF₆ was transferredinto a second vessel containing 20 ml of an ionic liquid (IL) using ametal spatula. Mass measurements were taken of the empty vial, the vialafter adding IL, and the vial after adding UF₆. The concentration inmolarity was obtained using the formula mass of the UF₆ and the volumeof IL. The sample was continuously stirred using a magnetic Teflon baron a stir plate. No manual shaking of the sample was utilized to enhancedissolution.

UV-Vis: The dissolved UF₆ sample was pipetted into a 1 cm path-lengthquartz cuvette until it was at least ¾ full. The cuvette was sealed witha screw-top cap.

Complete dissolution was seen within 3 hours for lower concentration(˜0.2M) and within minutes for higher concentration (1-1.5M) when usingmethylpropylpiperidinium bis(trifluoromethane (MPPiTFSI). When UF₆ wasintroduced to the ionic liquid evidence of a reduction was observed bythe transition from a white solid to a green solution. Higherconcentration samples formed a green precipitate. Without being bound bytheory, a potential mechanism for the dissolution was hypothesized asshown in the equation below.UF₆+2(CF₃SO₂)N:—→UF₆ ²⁻+2(CF₃SO₂)N.

The ILs that have been utilized include: N-trimethyl-N-butyl ammoniumn-Bis(trifluoromethanesulfonyl)imide (TFSI−),1-butyl-1-methylpiperidinium (BPPI) (TFSI−), methylpropylpiperidinium(TFSI−), and 1-methyl-1-propylpiperidinium (MPPI) (TFSI−).

This process was also tested in 1-butyl-3-methylimidazolium (BMI)tetrafluoroborate (BF₄ ⁻). However, dissolution was achieved after asignificantly longer period of time suggesting that the lack of lonepair slowed the dissolution. This was believed to be due to the lack ofa lone pair of electrons for the reduction of the UF₆, as shown in theproposed mechanism above.

Example 2: Electrochemical Recovery of Uranium from ILs

Electrochemistry: All electrochemical studies were performed with an Auworking electrode, Pt auxiliary electrode (Electrode Area ˜1.5× workingelectrode area), and an ionic liquid based Ag/Ag+ reference electrodestandardized versus the ferrocene redox couple. Cyclic voltammetry andconstant potential methods were utilized to characterize theelectrochemical properties of the UF₆ and achieve deposition.Depositions were conducted over a 24 hour period. In some instances,samples were subjected to two or three consecutive 24 hours periods ormultiple electrodes were used to obtain deposits from the same solution.

The dissolution process as described in Example 1, was used to dissolve˜0.5M UF₆ in MPPiTFSI for electrochemical recovery. The potential wasset at −3.0V for 24 hours. As shown in FIG. 1, black deposits are seenon the electrode which correspond with uranium deposits as shown byscanning electron microscopy.

The deposits were further analyzed by Energy Dispersive X-RaySpectroscopy (EDS) as shown in FIGS. 2A and 2B, which at higherresolution (500× magnification) showed uranium metal geometric crystals.Speciation analysis on the geometric crystals is shown in FIG. 3. Thegeometric crystals were found to consist almost entirely of uraniummetal. The baseline oxygen levels were consistent throughout, even inareas where there was no deposition of uranium crystals. Elementalanalysis of the deposits was completed, as shown in FIG. 5. Someresidual fluorine was detected.

Example 3: Precipitation from UF₆/IL

The dissolution process as described in Example 1, was used to dissolvegreater than 0.5M UF₆ in MPPiTFSI. Upon dissolution, a green precipitatewas observed. The precipitate was recovered using filtration followed byan acetone wash to minimize residual ionic liquid. The precipitationmethod utilizes an ionic liquid that comprises an anion with a lone pairof electrons, such that the reduced uranium hexafluoro anion forms asalt with the cation of the ionic liquid.

The precipitate was analyzed by powder X-ray diffraction (PXRD) (FIG.6). Peaks from the sample partially matched with those for a knownsample of UF₄(H₂O)_(1.5), suggestive that the precipitate includeduranium in the +4 oxidation state and not the +6 oxidation state.

Thermogravimetry analysis (TGA) (FIG. 7) was utilized to determine themetal content and the speciation based on correlation of mass loss andpossible chemical species (Table 1). Calculations were completed bycalculating the moles U in the sample following TGA/DSC and comparingthat to the calculated mass of the initial sample if those chemicalspecies listed in Table 1 were that of the initial sample. Multiplerepeats of the process and the analysis have shown consistent resultsfor the formation of a uranium hexafluoro anion salt with the cation ofthe ionic liquid.

TABLE 1 Gravimetric Analysis. Average mass loss of samples was 59.8 ±1.2%. Compound Average Error Std. Dev UF₃(TFSI)₃*3(MPPi) 131.5%  6.8%UF₄(TFSI)₂*2(MPPi) 71.7% 5.0% UF₅(TFSI)*MPPi 11.9% 3.3% UF₆*2(MPPi)−5.7% 2.8% UF₄(TFSI)*(MPPi)   9.1% 3.2% UF₄(TFSI)₂  29.5% 3.8%UF₂(TFSI)₂  23.9% 3.6%

As shown in FIG. 7, TGA analysis was consistent with the melting ofuranium metal from 1070.1° C. to 1142.4° C. This suggests thatwell-known methods for thermal treatment may be used to recover uraniummetal. In addition, PXRD analysis following TGA showed that heating inoxygen containing environments results in formation of UO₂ (FIG. 8). UO1indicated that the uranium and oxygen atoms are slightly less than a 1:2ratio. The sulfur in UOS was likely from residual TFSI. In either UO₂ orUOS, uranium is in the +4 oxidation state. Total mass of uraniumconfirmed the ratio of organic cation and inorganic U for thecalculation.

Conversely, when these experiments were completed under Argon, UO₂formation was not detected.

For reasons of completeness, various aspects of the invention are setout in the following numbered clauses:

Clause 1. A method for recovering uranium, comprising dissolving uraniumhexafluoride (UF₆) directly into an ionic liquid at concentrationsgreater than 0 M and less than or equal to 0.5 M; and applying apotential to the ionic liquid to deposit uranium onto an electrode as ametal.

Clause 2. The method of clause 1, further comprising chilling the UF₆prior to dissolving the UF₆ in the ionic liquid.

Clause 3. The method of clause 1 or clause 2, wherein the ionic liquidcomprises an anion with a lone pair of electrons.

Clause 4. The method of any of clauses 1-3, wherein the ionic liquidcomprises an anion selected from the group consisting ofn-bis(trifluoromethanesulfonylimide) (TFSI), dicyanomide,trifluoroacetate, alkyl sulfonates, alkyl sulfates,bis(fluorosulfonyl)imide and trifluoromethylacetate.

Clause 5. The method of any of clauses 1-4, wherein the ionic liquidcomprises n-bis(trifluoromethanesulfonylimide) (TFSI) anion.

Clause 6. The method of any of clauses 1-5, wherein the ionic liquidcomprises a cation that does not undergo reductive decomposition at apotential between −2 and −4 Volts.

Clause 7. The method of any of clauses 1-6, wherein the ionic liquidcomprises a cation selected from the group consisting ofalkyl-substituted or unsubstituted ammonium cations, alkyl-substitutedor unsubstituted piperidinium cations, and alkyl-substituted orunsubstituted pyrrolidinium cations.

Clause 8. The method of any of clauses 1-7, wherein the ionic liquidcomprises a cation selected from the group consisting oftetraalkylammonium cation, a dialkylpiperidinium cation, anddialkylpyrrolidinium cation.

Clause 9. The method of any of clauses 1-8, wherein the ionic liquidcomprises methylpropyl piperidinium cation.

Clause 10. The method of any of clauses 1-9, wherein the appliedpotential is more negative than −2 Volts.

Clause 11. The method of any of clauses 1-10, wherein the appliedpotential is pulsed.

Clause 12. The method of any of clauses 1-10, wherein the appliedpotential is constant.

Clause 13. A method for recovering uranium, comprising dissolvinguranium hexafluoride (UF₆) directly into an ionic liquid atconcentrations greater than or equal to 0.5 M to form a solidprecipitate in an ionic liquid solution; separating the solidprecipitate from the ionic liquid solution; and thermal processing.

Clause 14. The method of clause 13, wherein the thermal processing is inan inert atmosphere to form uranium metal.

Clause 15. The method of clause 13, wherein the thermal processing is inan ambient atmosphere to form uranium oxide, UO₂.

Clause 16. The method of any of clauses 13-15, further comprisingchilling the UF₆ prior to dissolving in the ionic liquid.

Clause 17. The method of any of clauses 13-16, wherein the ionic liquidcomprises an anion with a lone pair of electrons.

Clause 18. The method of any of clauses 13-17, wherein the ionic liquidcomprises an anion selected from the group consisting ofn-bis(trifluoromethanesulfonylimide) (TFSI), dicyanomide,trifluoroacetate, alkyl sulfonates, alkyl sulfates,bis(fluorosulfonyl)imide and frifluoromethylacetate.

Clause 19. The method of any of clauses 13-18, wherein the ionic liquidcomprises bis(trifluoromethanesulfonylimide) (TFSI) anion.

Clause 20. The method of any of clauses 13-19, wherein the ionic liquidcomprises a cation that does not undergo reductive decomposition at apotential between −2 and −4 Volts.

Clause 21. The method of any of clauses 13-20, wherein the ionic liquidcomprises a cation selected from the group consisting ofalkyl-substituted or unsubstituted ammonium cations or alkyl-substitutedor unsubstituted piperidinium cations.

Clause 22. The method of any of clauses 13-21, wherein the ionic liquidcomprises methylpropyl piperidinium cation.

Clause 23. The method of any of clauses 13-22, wherein the solidprecipitate comprises a salt of a uranium hexafluoro anion and an ionicliquid cation.

Clause 24. The method of any of clauses 13-23, wherein the ionic liquidsolution comprises uranium hexafluoride dissolved in the ionic liquid.

Clause 25. The method of any of clauses 13-24, further comprisingapplying a potential to the ionic liquid solution after separation ofthe solid precipitate to deposit uranium onto an electrode as a metal.

Clause 26. The method of clause 25, wherein the applied potential ismore negative than −2 Volts.

Clause 27. The method of clause 25 or clause 26, wherein the appliedpotential is pulsed.

Clause 28. The method of clause 25 or clause 26, wherein the appliedpotential is constant.

What is claimed is:
 1. A method for recovering uranium, comprisingdissolving uranium hexafluoride (UF₆) directly into an ionic liquid atconcentrations greater than or equal to 0.5 M to form a solidprecipitate in an ionic liquid solution; separating the solidprecipitate from the ionic liquid solution; and thermal processing thesolid precipitate.
 2. The method of claim 1, wherein the thermalprocessing is in an inert atmosphere to form uranium metal.
 3. Themethod of claim 1, wherein the thermal processing is in an ambientatmosphere to form uranium oxide, UO₂.
 4. The method of claim 1, furthercomprising chilling the UF₆ prior to dissolving in the ionic liquid. 5.The method of claim 1, wherein the ionic liquid comprises an anion witha lone pair of electrons.
 6. The method of claim 1, wherein the ionicliquid comprises an anion selected from the group consisting ofn-bis(trifluoromethanesulfonylimide) (TFSI), dicyanomide,trifluoroacetate, alkyl sulfonates, alkyl sulfates,bis(fluorosulfonyl)imide and frifluoromethylacetate.
 7. The method ofclaim 1, wherein the ionic liquid comprisesbis(trifluoromethanesulfonylimide) (TFSI) anion.
 8. The method of claim1, wherein the ionic liquid comprises a cation that does not undergoreductive decomposition at a potential between −2 and −4 Volts.
 9. Themethod of claim 1, wherein the ionic liquid comprises a cation selectedfrom the group consisting of alkyl-substituted or unsubstituted ammoniumcations or alkyl-substituted or unsubstituted piperidinium cations. 10.The method of claim 1, wherein the ionic liquid comprises methylpropylpiperidinium cation.
 11. The method of claim 1, wherein the solidprecipitate comprises a salt of a uranium hexafluoro anion and an ionicliquid cation.
 12. The method of claim 1, wherein the ionic liquidsolution comprises uranium hexafluoride dissolved in the ionic liquid.13. The method of claim 12, further comprising applying a potential tothe ionic liquid solution after separation of the solid precipitate todeposit uranium onto an electrode as a metal.
 14. The method of claim13, wherein the applied potential is more negative than −2 Volts. 15.The method of claim 13, wherein the applied potential is pulsed.
 16. Themethod of claim 13, wherein the applied potential is constant.